Martin P. Day

Clinical and biological materials, foods and beverages

This Update refers to papers published approximately between September 2005 and August 2006. In a new development we have introduced a section specifically to discuss the emerging field of metallomics. This allows the inclusion not just of the essential analytical work but also applications involving the structural and functional roles of metals and metalloids. This work is directed towards understanding the metabolism of elements, their involvement in the biochemistry of molecules such as proteins and nucleic acids, and their mechanisms of action. In the period covered by this review we can see the development of several elegant but complex methods to provide for an integral approach which links the quantitative analysis with information about structural and functional activity. At a time when analytical equipment is so sophisticated it should not be necessary to ask questions on the validity of published results. However, as those who review submitted papers will appreciate, this can never be taken for granted and it has been demonstrated that the quality of data (judged by the spread of ‘normal results’) is related to the attention devoted to quality control in the written report. A number of new pieces of work were seen in this review period. Use of exhaled breath as a novel biological sample type was reported. A preconcentration column located in the arm of an autosampler used for ETAAS was applied to measurements of Pt in foods and beverages. Interferences associated with the determination of Cd in urine by ETAAS were removed with a neat piece of manipulation. The sample was placed in the furnace and Cd concentrated onto Pd modifier using an electrolytic process, after which the sample solution, together with interferents, was drawn back into the capillary and sent to waste. The popularity of ICP-MS continues to grow, largely fuelled by collision cell applications and by work on getting the right gas for the job. Following on from the considerable Pb in bone work achieved with in vivo XRF, this technique is now being used to measure Cd, although the sensitivity requires improvement if normal concentrations are to be determined. Work on selenium is as popular as ever in both the clinical and food areas, with several reviews seen and fundamental work on sample stability, extraction, speciation, bioavailability, and the identification of novel compounds in yeast and other samples, many of which involve Se/S substitutions. Selenosugars are recognised as important metabolites and now arsenosugars have been identified. In recent years we have looked without much success for data related to organically produced food but now there are some data for milk. Of 45 elements measured, Mo was increased while Ba, Eu, Mn and Zn were reduced, when compared with conventional cow’s milk. Among the more unusual studies seen were measurements of Pb in alligator bones and essential elements in royal jelly.

Designing and creating Saccharomyces interspecific hybrids for improved, industry relevant, phenotypes

To remain competitive in increasingly overcrowded markets, yeast strain development programmes are crucial for fermentation-based food and beverage industries. In a winemaking context, there are many yeast phenotypes that stand to be improved. For example, winemakers endeavouring to produce sweet dessert wines wrestle with fermentation challenges particular to fermenting high-sugar juices, which can lead to elevated volatile acidity levels and extended fermentation times. In the current study, we used natural yeast breeding techniques to generate Saccharomyces spp. interspecific hybrids as a non-genetically modified (GM) strategy to introduce targeted improvements in important, wine-relevant traits. The hybrids were generated by mating a robust wine strain of Saccharomyces cerevisiae with a wine isolate of Saccharomyces bayanus, a species previously reported to produce wines with low concentrations of acetic acid. Two hybrids generated from the cross showed robust fermentation properties in high-sugar grape juice and produced botrytised Riesling wines with much lower concentrations of acetic acid relative to the industrial wine yeast parent. The hybrids also displayed suitability for icewine production when bench-marked against an industry standard icewine yeast, by delivering icewines with lower levels of acetic acid. Additionally, the hybrid yeast produced wines with novel aroma and flavour profiles and established that choice of yeast strain impacts on wine colour. These new hybrid yeasts display the desired targeted fermentation phenotypes from both parents, robust fermentation in high-sugar juice and the production of wines with low volatile acidity, thus establishing their suitability for wine styles that are traditionally troubled by excessive volatile acidity levels.

White wine taste and mouthfeel as affected by juice extraction and processing.

The juice used to make white wine can be extracted using various physical processes that affect the amount and timing of contact of juice with skins. The influence of juice extraction processes on the mouthfeel and taste of white wine and their relationship to wine composition were determined. The amount and type of interaction of juice with skins affected both wine total phenolic concentration and phenolic composition. Wine pH strongly influenced perceived viscosity, astringency/drying, and acidity. Despite a 5-fold variation in total phenolics among wines, differences in bitter taste were small. Perceived viscosity was associated with higher phenolics but was not associated with either glycerol or polysaccharide concentration. Bitterness may be reduced by using juice extraction and handling processes that minimize phenolic concentration, but lowering phenolic concentration may also result in wines of lower perceived viscosity.

Effect of Commercial-Scale Filtration on Sensory and Colloidal Properties of Red Wines over 18 Months Bottle-Aging

Filtration is essential for red wine stability, but its effect on wine colloids and sensory properties, such as texture, remains a concern. Small-scale investigations have demonstrated loss of color and polysaccharides; however, the effect of commercial-scale filtration on red wines is unknown. Samples of four commercial wines (Cabernet Sauvignon and Shiraz from 2013 and 2014 vintages) were collected from two commercial bottling facilities before and after crossflow filtration and lenticular filtration, after 0.65-μm membrane, and after 0.45-μm membrane filtration. Cabernet Sauvignon 2014 wines were filtered through polyether sulfone or nylon 0.45-μm membranes. The average size of particles in all wines decreased significantly with crossflow filtration. The concentration of polysaccharides decreased with 0.45-μm filtration, while tannin and color remained unchanged. After 18 months of bottle aging, the average particle sizes of filtered and unfiltered 2013 wines were similar, whereas the filtered 2014 wines contained smaller particles than the unfiltered 2014 wines. Sensory analysis showed no consistent filtration-related trends in textural attributes across all wines, although there were some significantly different aromas or flavor attributes for samples of different filtration grade within each wine. These results suggest that commonly applied commercial filtration practices do not affect wine color and have a minimal effect on sensory profiles of red wines.